This invention pertains to an improved electrical formation heating and viscous oil producing process. More particularly, in an electrical heating, oil producing process, controlled pressure aqueous fluid flow between a closely spaced well pair is used to significantly increase the effective radius of an oil production location. The production well pair is also used as a combined enlarged formation heating electrode.
Large relatively shallow deposits of viscous hydrocarbonaceous substances whose viscosity is decreased by heat are known to exist in subterranean formations. Many techniques have been proposed for producing oil from the viscous oil bearing formations. It has been proposed, for example, in U.S. Pat. Nos. 3,642,066; 3,874,450; 3,848,671; 3,931,856; 3,948,319; 3,958,636; 4,010,799; and 4,084,637, to use electrical current to add heat to a subsurface pay zone containing viscous oil. Electrodes are connected to an electrical power source and are positioned at spaced apart points in contact with the earth, for example, in the formation. Electrical current flow through the formation heats the oil by electric power dissipation. Frequently, in electrical well heating, most of the energy is dissipated near the electrode surfaces. It has been suggested that saltwater be injected to increase the effectiveness of a subsurface electrode. For example, in U.S. Pat. No. 3,931,856 salt water is injected between an injection well and satellite wells to increase the effective size of an electrode injection well. This process involves injection pressures above the formation pressure and does not pertain to increasing the effective radius of a producing location.
Oil production depends on a driving force or pressure differential between the formation and the producing well. As oil is produced from the formation, this driving force is depleted and oil production may stop. It has been proposed to inject various fluids which will maintain the pressure of the formation and drive the oil toward the producing well. During oil production, the greatest pressure drop occurs as the oil approaches the wellbore. Reservoir calculations use a concept called the effective radius of the borehole. Various techniques have been proposed to increase the effective radius of a producing location. For example, it has been proposed to create highly conductive fractures in the formation to increase the effective radius of a producing well. Fracturing requires injection pressures above the formation pressure. Moreover, viscous oil bearing formations are typically unconsolidated and fractures rapidly close and seal themselves if the injection pressure is decreased. It has been proposed to prop fractures with various forms of solid propping agents in a manner such that the fracture retains some of its relatively high conductivity to fluid flow. But in unconsolidated formations, fracture propping is difficult to achieve successfully. The unconsolidated tar-like nature of the walls of the fracture will simply close around and extrude into pores between the multilayers of propping agents, thereby sealing the fracture.
It is the primary objective of this invention to provide an improved method of increasing the effective radius of a production location in a way that does not require continued use of injection pressures above the pressure of the formation forcing oil toward the production location.